I have this idea in my head that higher amp'age alternators need to run at a higher RPM to charge properly. I seem to remember a mate of mine owning a V8 Statesman with a 100amp alternator, and if he let the car idle at 700rpm with the sound system going, the battery would eventually die.
yep
i got a 140A alternator and it doesnt charge unless its sitting on 900 rpm or more. lol, was tuning it the other day (block of wood between the brake pedal and seat and in drive cos an auto) and cos' the revs were down to around 5-600 im tuning, tuning, lala alaal, oh dear turned the screw too far and the engine dies... 'no worries, just put it back in park and start her up'
nope. drained all the juice from the battery and had to jump start her...
pain in the arse. no idea why it does it. the pulley is the exact same size as a stock one. weird.